1. Field of the Invention
The present invention relates to a resonance tone generating apparatus for generating resonance tones of musical signals and an electronic musical instrument provided with the resonance tone generating apparatus.
2. Description of the Related Art
An electronic musical instrument is well known, which is provided with a damper pedal and changes a musical tone in response to operation of pressing down the damper pedal. In particular, resonance tone adding apparatuses are proposed, which generate resonance tone data based on musical signal data and add the generated resonance tone data onto the musical signal data in response to operation of the damper pedal.
In general, the above resonance tone adding apparatus receives digital musical signal data and performs a filtering process on the received musical signal data using a digital filter, thereby generating resonance tone data. In the filtering process, FIR (Finite Impulse Response) filter and/or IIR (Infinite Impulse Response) filter are used.
When FIR filter is used, a convolution operation is performed on supplied musical signal data x(n−k), where “k”=0, 1, . . . , (n−1), and impulse response data a(k) acquired from reverberation characteristics of a concert hall, whereby resonance tone data Y(n)=Σ×(n−k)×a(k) can be obtained.
U.S. Pat. No. 5,569,870 discloses an electronic musical instrument that changes an envelop of musical signal data depending on a position of a pressed damper pedal, and generates a musical tone particularly when the damper pedal is pressed down half way.
Japanese Patent No. 2,692,672 discloses a technique, in which a resonance tone generating apparatus generates resonance tone data RWD based on waveform data SWD corresponding to a musical tone waveform, and a multiplier adjusts an amplitude level of the waveform data AWD to decrease during the course of pedal data increasing from the minimum value “0” to the maximum value “1”, wherein the pedal data indicates how much the damper pedal has been pressed down and is detected when said damper pedal is pressed down, and further the multiplier adjusts the resonance tone data RWD generated by the resonance tone generating apparatus to increase.
Particularly, resonance tones of a piano are complex and a technique for generating resonance tones of piano strings has been proposed.
In Japanese Patent Application No. 2007-193129 A is proposed a technique that is provided with groups of plural string resonance circuits (digital filters) each having resonance frequencies corresponding to harmonic tones of each letter notation and performs the convolution operation on data output from each string resonance circuit, thereby generating a resonance tone similar to a string resonance tone of the piano.
In electronic musical instruments, resonance tones including reverberation sounds generated when the damper pedal is pressed down cannot be reproduced simply by changing an envelop of musical signal data as disclosed in U.S. Pat. No. 5,569,870.
Further, in the technique disclosed in Japanese Patent No. 2,692,672, a mixing ratio of the musical tone to resonance tone is changed by a so-called cross-fade technique, but the technology has a disadvantage that, since the resonance tone itself does not change, change of the resonance tone due to pressing operation of the damper pedal is poor.
Further, in the technique disclosed in Japanese Patent Application No. 2007-193129 A, since plural string resonance tone generating circuits are provided for each keyboard zone, such disadvantage is invited that a large scale of circuit is required. Further, since the resonance tone is not produced in consideration of a piano structure, another disadvantage is invited that a sufficient resonance tone cannot be reproduced even though the large scale of circuit is employed.